The anterior cruciate ligament (ACL) originates from the medial aspect of the lateral femoral condyle and is inserted into the tibial plateau medial to the anterior horn of the lateral meniscus.
The ACL is a strong structure that has an important role in stabilising the knee. It is often injured, especially during sports activities, and does not usually heal. Because of these factors, it is usual for a ruptured ACL to be treated by reconstructive surgery, when a tendon graft is usually used to replace the damaged ACL. In conventional ACL reconstruction, a single graft structure is made: either a strip of the patellar tendon, or else a composite structure consisting of usually four strands of hamstrings tendons are used. This graft is placed inside the knee joint, replacing the ACL. It is hoped that it will heal in place and remodel into a new ACL.
In order to fix the new graft in place, it is usual for the surgeon to drill a graft tunnel at the attachment site in both the femur and tibia. These tunnels are usually placed at the anatomical attachment areas of the damaged ACL. During surgery, the graft is pulled into these tunnels and secured; many devices have been developed to anchor these grafts.
The principal reason for ACL reconstructive surgery to fail is malplacement of the graft fixation tunnels. That occurs because the ACL is placed awkwardly within the knee joint, and it is difficult to judge the exact positions needed, even when looking through a modern arthroscopic camera system. Recognising this, surgical instruments have evolved to try to make the choice of tunnel position less subjective, but that approach has not developed to the point where errors are avoided.
A further factor is that the ACL has a complex fibre bundle structure, with many fibre fascicles that attach over quite large areas on the bone surfaces. This leads to individual fibres having different lengths. They also have different patterns of tightening and slackening as the knee flexes and extends, or as the tibia rotates about its long axis. Recognising this, there has recently been a development of ‘double-bundle’ reconstruction methods. This usually involves making two tunnels in each bone, and using two grafts. These are a crude approximation of two main areas of fibres in the cross-section of the ACL [Fakhry G &.Girgis. T. Clin Orthop 1975; 106]. These bundles are normally called the ‘anteromedial’ AM bundle (or AMB) and ‘posterolateral’ PL bundle (or PLB). These names relate to their relative positions of attachment to the tibial plateau. In general, it has been found that the PLB tightens as the knee is extended, while the AMB is tightest in the flexed knee [Xerogeanes J W. et al. Knee Surg Sports Traumatol Arthrosc 1995; 3: 9-13, Sakane M. J Orthop Res. 1997; 15: 285-293, Bach J M. et al. J Biomech. 1997; 30: 281-283]. Thus, they have distinct stabilising roles. The underlying principle of double-bundle surgery is that it more closely reproduces the natural ACL anatomy, and also functions closer to the natural ligament than does a single-bundle reconstruction. Isometric reconstructions reproduce the anteromedial bundle, but the knee needs stability in the functional posture, which is when it is weight-bearing near extension, ie the posterolateral bundle is then needed.
Surgical methods of ACL reconstruction following injury have developed considerably over the last 15 years. Primary repair and extra-articular procedures have failed to reproduce satisfactory stability of the knee [Grontvedt T. et al. J Bone Joint Surg [Am] 1996;78-A: 59-68] and the use of prosthetic ligaments has been abandoned [Frank C. & Jackson D W. J Bone Joint Surg [Am] 1997;79-A:1556-76]. These techniques have been superseded by reconstruction with an intra-articular graft. Hence, the current surgical approach is by anatomical reconstruction using a biological tissue autograft. The bone-patellar tendon-bone graft B-PT-B has given good clinical results [Corry I. S. et al. Am J Sports Med 1999;27:444-53] but morbidity at the donor site [Christen B. & Jakob R P. J Bone Joint Surg [Br] 1992;74-B:617-19, Kartus J. et al. Knee Surg Sports Traumatol Arthrosc 1997;5:222-8] has prompted many surgeons to favour a four-strand hamstring graft, usually using the tendons of semitendinosus and gracilis doubled.
Radford and Amis [J Bone Joint Surg Br 1990; 72: 1038-1043] reported that a double-bundle reconstruction controlled anterior laxity better than single-bundle reconstructions, across the range of knee flexion. Yagi et al [Am J Sports Med. 2002; 30: 660-666] reported finding the biomechanical outcome, especially in rotatory loading, may be superior with double bundle reconstructions compared to single bundle reconstructions, and Mae et al [Arthroscopy 2001; 17: 708-716] similarly found better antero-posterior stability using a two femoral socket technique when compared to the standard single socket ACL reconstruction. Mommersteeg et al [J Anat 1995; 187: 461-471] suggested that successful ACL reconstruction may not be achieved simply by replacing one bundle. Conventional endoscopic ACL graft placement does not always control tibial rotation laxity, leaving a residual ‘mini-pivot’ [Bull AMJ. et al. J Bone Jt Surg 84Br: 1075-1081, 2002]. The realisation that anterior laxity is not an adequate measure of success of an ACL reconstruction, and that rotatory laxity is important has led to a sudden widespread interest in double-bundle methods, [Amis AA et al. Operative Methods in Sports Med 15; 29-35, 2005].
Race & Amis developed a double-bundle PCL reconstruction method [J Bone Jt Surg 80B, 1998; 173-179] that was widely adopted, partly because it was also shown clearly that: a) the PCL was not an isometric ligament; b) that isometric PCL reconstructions gave less effective control of tibial posterior laxity.
ACL reconstruction aims to recreate the exact mechanical properties of the injured ligament and restore normal function to the knee. Currently, this cannot be achieved. Biomechanical testing of ligament reconstructions in the laboratory has been used widely in attempts to recreate these mechanical properties. Although the ultimate load to failure of the B-PT-B and that of the four-strand hamstring graft exceed those reported for the intact ACL, it is accepted that in the early postoperative period it is the fixation of the graft which is the weak link [Kurosaka M. et al Am J Sports Med 1987;15:225-9].
ACL fixation may be either mechanical or biological. The emphasis on accelerated programmes of rehabilitation and demands for a rapid return of function necessitate secure mechanical fixation in the early post-operative period before biological fixation has occurred by healing in the graft tunnel.
As ACL reconstruction techniques evolve, an accurate and useful description of the attachment anatomy is required in order to design instruments capable of placing graft tunnels so that their entrances are in anatomically correct locations, within the ACL attachments. Anatomical descriptions of the attachment anatomy of the two bundles of the ACL using methods that can be employed clinically are lacking. An accurate map of the attachment of the ACL on the femur is key for the development of double bundle techniques and in outcome studies to describe optimal and suboptimal positions for graft placement.
The importance of femoral tunnel placement in ACL reconstruction has previously been reported with respect to a single graft bundle technique [Amis A A. & Jakob R P. Knee Surg Sports Traumatol Arthrosc 1998; 6 Suppl 1: S2-12]. Sommer [Knee Surg Sports Traumatol Arthrosc 2000; 8: 207-213] found a significant correlation between the femoral single bundle placement and the International Knee Documentation Committee IKDC score. As the placement of the graft as seen on X-ray moved away from the most isometric point, the IKDC scores decreased. It will be just as critical to achieve optimum graft placement in the double bundle technique as it is in the single bundle technique.
EP0361756 describes a device that measures changes in distance between chosen points on femur and tibia. It does not assist the surgeon in identifying anatomical locations for graft tunnels; instead it helps to identify points that are a constant distance apart when the knee flexes i.e. points that are “isometric”.
EP0440991 A1 also refers to finding an ‘isometric’ point. It also describes a new type of drill for making a hole of known depth. A tibial drill guide is also described. However this device relies entirely on the surgeon's judgement for placement within the knee. A feature of this device is that the guide barrel can slide towards the bone until its sharp tip engages the bone, thereby stabilising the drill guide in the chosen position. This feature is common to many types of drill guides.
EP0495487 A2 discloses a drill that, instead of just boring out a hole through the bone, cuts it out as a solid core, for use elsewhere in the operation. A “guide for locating a pilot hole on the femoral condyle” is cited but this is a bone coring/drilling method, there is no assistance given to place the tunnel accurately.
U.S. Pat. No. 4,883,048 discloses a feature that is used widely, namely the use of an arcuate feature to allow the drill to be guided through a tube to a fixed point from a range of directions. However, the choice of precisely where to drill is still surgeon-dependent; instrument does not locate the optimal site.
U.S. Pat. No. 5,269,786 and U.S. Pat. No. 5,409,494 use the arcuate feature. They describe a drill guide that does aim to locate the correct place for a graft tunnel, but it does so by locating on another ligament, the PCL, and does not utilise bony features. The PCL is a soft tissue structure and so is inherently inaccurate as a datum.
In U.S. Pat. No. 6,019,767 and U.S. Pat. No. 5,300,077 is described a device whose principle is that the axis of the drill guide is aligned parallel to the probe tip that rests on the roof of the femoral intercondylar notch. Thus, it ensures that the graft will not impinge against the notch roof. It therefore locates the tibial drill hole in relation to the femur. It does not address the femoral tunnel location.
U.S. Pat. No. 5,350,383 also uses the arcuate feature but attempts to ‘invert’ the moving feature. Once again the surgeon judges where to place the drill target.
U.S. Pat. Nos. 5,520,693, 6,352,538 and 6,878,150 give a device that has a tongue protruding from the body of the drill guide that locates on an edge of the bone, ensuring that the drill axis is located a certain distance from that edge. However, it does not identify where to go along the edge of the bone—only one direction/dimension is controlled. The surgeon usually places the probe or tongue at a chosen “o'clock” position in the femoral notch.
U.S. Pat. No. 5,603,716 describes a means of locating tunnel positions using an aimer referenced to anatomical structures within the knee. It is a method for drilling a socket in the tibia but it does nothing to identify exactly where the socket should be situated.
The devices provided by U.S. Pat. No. 6,254,604 and U.S. Pat. No. 6,254,605 are similar to U.S. Pat. No. 5,300,077 but the latter adds a removable guide bar to provide visual alignment in the coronal plane. This principle being that, if the bar is held horizontal, then the drill guide will slant across the tibia in a preferred orientation. This guides the tunnel orientation.
The basis of the device in EP0384098 is that it combines two drill guides in one instrument, with a fixed relationship between them, intending to create tibial and femoral tunnels at the “correct” places in the knee. It has a hook that locates over the posterior edge of the tibia. The tibial tunnel is always on the midline while the femoral tunnel guide can be swung to left or right for an oblique tunnel in left or right knees. The femoral tunnel is located in relation to the hook on the tibia.
GB 2 268 688 provides a device for locating tibial tunnels. The device is simply placed into the knee at an angle to the midline plane, so that its probe passes to one side of the patellar tendon. Bends are introduced into the instrument, to allow the probe tip to be straight along the midline plane, while the body of the drill guide is held at an oblique plane outside the knee.
U.S. Pat. No. 4,257,411 describes a drill guide adapted to clamp securely onto the bone. It has no features that locate the tunnel in relation to the anatomy.
U.S. Pat. No. 5,112,337 describes a further device for tibial tunnel placement. It relies on surgeon's judgement of where to drill the hole, by placing a target tip. It has an arcuate adjustment to vary the tunnel orientation. It also allows the drill guide to slide until its tip engages the bone. The sliding drill guide has length marks so that the surgeon can choose a desired tunnel length.
U.S. Pat. No. 4,823,780, EP0162027 and U.S. Des 289,436 provide a device for making tunnels that are in a fixed relationship in space. The device requires surgeon's judgement for placing it correctly in the knee, it has no location features.
A study of graft tunnel positions following endoscopic single-bundle ACL reconstructions performed by surgeons in Europe revealed a need for major improvement in ACL reconstruction instrumentation, a principal aim being to reduce the subjective element of judgement of instrument positioning prior to drilling bone tunnels [Kohn D. et al in Knee Surg. Sports Traumatol. Arthrosc. 6 Suppl 1: S13-S15, 1998].
The present invention aims to address two unmet clinical needs: Firstly, the frequent failure of ACL reconstructions, which is mostly caused by misplacement of the graft tunnels and, secondly, the residual rotatory laxity remaining after conventional endoscopic ACL reconstruction of the knee.
The inventors have measured the location and extent of the femoral and tibial attachments of the ACL. A range of different measurement systems has been used, reflecting methods published previously. Some of the measurement methods have been modified in order to make them more relevant to arthroscopic surgery. This work included measurement of the centres of both the entire ligament and also of the individual fibre bundle attachments. The attachment locations have been related to bone landmarks suitable for locating instruments.